feat: UX improvements — nav, reports tabs, dashboard alerts, transaction hints, settings layout

- Move Reports to Finans nav group and auto-expand Övrigt on its pages
- Make report tabs horizontally scrollable with gradient fade on mobile
- Surface deadlines and alerts above the fold on dashboard
- Add dismissible categorization hint card on transactions page
- Split settings company form into 4 separate Cards for scannability
- Add monthly breakdown report, document upload zone, journal entry attachments
- Add batch category selector, receipt document linking, invoice form improvements

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/api/reports/monthly-breakdown/route.ts

@@ -0,0 +1,26 @@
+import { createClient } from '@/lib/supabase/server'
+import { NextResponse } from 'next/server'
+import { generateMonthlyBreakdown } from '@/lib/reports/monthly-breakdown'
+
+export async function GET(request: Request) {
+  const supabase = await createClient()
+  const { data: { user } } = await supabase.auth.getUser()
+
+  if (!user) {
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
+  }
+
+  const { searchParams } = new URL(request.url)
+  const periodId = searchParams.get('period_id')
+
+  if (!periodId) {
+    return NextResponse.json({ error: 'period_id is required' }, { status: 400 })
+  }
+
+  try {
+    const data = await generateMonthlyBreakdown(user.id, periodId)
+    return NextResponse.json({ data })
+  } catch {
+    return NextResponse.json({ error: 'Failed to generate monthly breakdown' }, { status: 500 })
+  }
+}